Publications and other reference materials referred to herein are numerically referenced in the following text and respectively grouped in the appended Bibliography which immediately precedes the claims.
Nanoscience and nanotechnology have attracted unprecedented interest and effort in the past decade from many scientific disciplines, such as physics, chemistry, materials sciences and others, making them into exciting multidisciplinary subjects. Highly multidisciplinary efforts have resulted in substantial progress and a broad spectrum of scientific and technological accomplishments, with many more expected. Nanotechnology is expected to play a pivotal role in the world economy in years to come.
The remarkable progress in nanoscience and nanotechnology has created the need for practical tools capable of resolving and analyzing nanometer scale structures. Analytical and imaging tools that have spatial resolution at the nanometer scale are of paramount importance for both fundamental nanoscience and applied nanotechnology [1]. In fact, any progress in the synthesis and study of novel nanostructures is ultimately related to, and often limited by, our ability to probe and analyze them. However, most imaging and analysis tools in use today are not adequate for addressing these emerging challenges at the nanoscale.
Another scientific frontier that has witnessed explosive progress in the past decade is high harmonic generation (HHG) and attosecond science [2]. The recent spectacular progress in advanced femtosecond laser technology has opened the door to the attosecond world. This allows real-time experimental observation and time domain control of atomic scale electron dynamics in matter. Despite this remarkable progress, several fundamental challenges in attosecond science, some of which will be addressed by the present invention, remain unsolved.
High harmonic generation, being the backbone of attosecond science, possesses a unique combination of properties, not only in the temporal but also in the spectral domain, which could be very attractive in studies of matter at the angstrom and nanoscales. High harmonics' short wavelength, spatial coherence [3] and a broad controllable spectrum makes them extremely interesting in the exploration of nano-structures and nanomaterials.
In recent years, significant effort has been directed towards the development of different types of electron microscopy, which is the main tool used in nanoscience today [4]. Although providing very valuable insight, most of this work is limited to surface (2D) imaging of the nanostructures. XUV and soft x-rays not only complement electron microscopy but also offer new contrast mechanisms for structural imaging and dynamics studies. Many nations have put tremendous effort and financial resources into developing synchrotrons and free electron laser systems (FEL), which are the main sources of XUV and X-ray radiation in use today.
The benchmark resolution (about 15 nm) has been obtained by imaging with 1.52 nm wavelength radiation from a third generation synchrotron light source [1]. The light source used in this experiment was the third generation synchrotron Advanced Light Source (ALS) in Berkeley. In this impressive one hundred million dollar facility, highly accelerated relativistic electrons are “stored” in a 200-meter storage ring, guided by a series of magnets that force them into a curved trajectory. As they travel around the storage ring, the electrons emit synchrotron radiation energy in the form of photons, which is directed by specialized optics down 12-meter long beamlines to experiment terminals.
Another example of an experimental facility capable of nanoscale and atomic imaging is the Linac Coherent Light Source (LCLS) based in the recently upgraded Stanford Linear Accelerator Center (SLAC). This is a free electron laser seeded by the SLAC linear accelerator; it emits hard X-rays, which are about a billion times brighter than the “traditional” synchrotron X-ray sources. The whole “set-up” occupies more than 1.7 square kilometers of land, being more than 3 kilometers long. More than 250 million dollars were required solely of upgrading the SLAC.
Nevertheless, the widespread use of XUV and soft x-ray light for investigating various types of imaging modalities requires the development of compact, so-called table-top systems. High-harmonics generation provides a very attractive source of ultra-short coherent radiation in the deep UV and soft x-ray range of the electromagnetic spectrum and has the inherent advantage that it is practically realizable on a laboratory scale, as opposed to large and very expensive free electron laser and synchrotron facilities.
Recently, several attempts have been made to exploit high harmonics for imaging. In diffractive imaging [5, 6], static, not spectrally resolved, two-dimensional imaging has been demonstrated with a resolution of the order of 100 nm. The technique uses over-sampling of the diffraction pattern with an iterative phase retrieval algorithm. In the so-called “ankylography” modality [7], an attempt has been made to obtain a three dimensional structure of an object from single “2D spherical pattern” that “is sampled at a sufficiently fine scale on the Ewald sphere”. Nevertheless, the imaging principles and proposed methodology of “ankylography” were found to be flawed, bringing into question its validity and scope of applicability [8].
In another work, Optical Coherence Tomography [11] was shown to be used with XUV radiation [10-12] that in principle should allow access to depth information from the samples. However, such a straightforward implementation of the visible light OCT approach to the XUV spectral range has significant limitations. First, due to lack of high quality optics (high reflection optical quality (at XUV wavelength) mirrors, beam-splitters, etc., particular focusing optics, it is impractical to get high lateral resolution. In addition, it was found that different harmonics (i.e. different wavelengths) typically have significantly different wavefront curvatures [13], thus different harmonics can't be focused to the same diffraction limited spot by conventional lens or mirrors.
Progress in nanoscience and nanotechnology as well as in biomedicine and structural biology depends not only on static examination of the surfaces of structures but also on seeing deep inside material structures to identify what they are made of. It is also very important to be able to follow the dynamic processes inside samples of interest so as to understand what electronic, magnetic, optical, chemical and mechanical processes may be in play and to understand their role.
It is therefore a purpose of the present invention to provide a system and method for performing multispectral multidimensional nanotomography with high harmonics and attosecond pulses capable of measuring the spectral properties of a sample.
It is a purpose of the present invention to provide a system and method for performing multispectral multidimensional nanotomography with high harmonics and attosecond pulses capable of providing visualization of temporal processes in a sample.
It is a purpose of the invention to provide a system and method for performing five dimensional multicolor holographic nano-tomography and optical coherence tomography with high harmonics and attosecond pulses.
Further purposes and advantages of this invention will appear as the description proceeds.